It is common in computer systems to represent and convey information through graphic representations. These representations may take a variety of forms, such as alphanumeric characters, various sorts of graphs, as well as images of physical objects rendered on various computer output devices, such as display video displays or printers. Historically, humans have controlled computer systems through keyboard entry of discrete commands, and entered data through keyboard data entry. Such commands or data are typically comprised of letters, numbers, and symbols. It has been discovered, however, that the ease of using computerized systems is generally a function of how close the system models the logical thought of its human user. A person can absorb and manipulate information placed in a visual or graphical context much faster than if the same information is represented merely by alphanumeric text. As a result, in recent years, interfaces for computer systems have been developed that more closely model what is expected by their human users, taking advantage of benefits associated with the visual or graphical display of information to make such systems easier to learn and use. These are often known as WYSIWYG (What-You-See-Is-What-You-Get) or GUI (Graphical-User-Interface) interfaces. Providing for computer control and data entry by a variety of means other than through keyboard entry, such as by mouse, joystick, trackball, or light pen, these interfaces have gone a long way to make user accessibility to computer data and its manipulation a reality.
Beyond simply controlling the computer and entering data, however, it is frequently desirable to see graphically the data entered, and in particular to see the interrelationship of this data. One way of accomplishing this has been the development of spreadsheet programs for use on computer systems that provide for data, such as numbers, to be entered into the computer system and subsequently displayed in graphic form. The numbers entered are initially represented by alphanumeric characters stored in a multiplicity of cells identified by a row and column address on the video display. Subsequent manipulation of data disposed in these spreadsheet programs typically requires the user to enter data into the cells by typing the numbers on a computer keyboard. To see the interrelationship of these numbers in graphic form, the numbers are output as a graph. Should the shape of the graph not be to the liking of the user of the computer system, or should the user desire to change the interrelationship among the numbers represented by the graph, new numbers must be typed into the cells of the spreadsheet, at which time the graph shape may change to reflect the change made to the numbers. While the data generally can be simultaneously displayed on the same computer video display as both alphanumeric characters and as a graph, the requirement that the user enter data on the keyboard renders the operation of the spreadsheet more difficult, and slows the user's quest for ultimate results, namely the manipulation of the interrelationship among the data to achieve the desired graph shape.